Signal and Train ControlRULES, STANDARDS, AND INSTRUCTIONS (R,S&I)

STC – 4

Interlocking Systems

Subpart D

Signal and Train Control - Rules, Standards, and Instructions (R,S&I) governing the installation, inspection, maintenance, and repair of Traffic Control Systems.  Subpart A rules apply to traffic control systems, as do some Subpart B and C rules.  This presentation will review those rules that apply to traffic contorl systems as well as introducing Subpart D rules that specifically apply to these systems.

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Learning Objectives
        - Understand that these regulations are engineering design standards and must be incorporated into the design of any TCS system.
        - Understand that actions taken during the installation, maintenance, or modification of the system must not negate these design standards.	

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The purpose of a Traffic Control System (TCS) is to improve the safe and efficient movement of trains by combining the characteristics of interlockings with automatic block signals.  With the addition of a communications system the system is capable of being controlled from a central location.  These systems are sometimes refered to as Centralized Traffic Control. 

CAUTION

The following presentation was developed to provide general information only. For detailed compliance information please refer to 49 CFR 236 – Rules, Standards and Instructions, Subpart D and the S&TC technical manual.  It is recommended that each employee refer to appropriate manuals and regulations when dealing with any specific issue.

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When in doubt, go to the book!

Information

The FRA Rules, Standards, and Instructions are considered to be the minimum standard allowed for the installation, inspection, maintenance, and repair of signal and train control systems, devices, and appliances.  Each railroad may adopt more stringent standards. Refer to your railroad’s signal standard and instruction manual for further guidance.

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Traffic Control System - 1927
        - This machine controlled the first traffic control system.  It was installed at Fostoria, Ohio and controlled the New York Central main track from Stanley to Berwick.
        - Single track TCS can

handle more traffic

than double track ABS.
        - The machine is now at

the Smithsonian 

Institute.

The General Railroad Signal Company (GRS) installed the first traffic control system on the New York Central in 1927.  GRS named their TCS system Centralized Traffic Control (CTC) and the name stuck.  CTC is now the generic name for what is technically a traffic control system.

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Traffic Control System Definition

§ 236.828 System, traffic control.

A block signal system under which train movements are authorized by block signals whose indications supersede the superiority of trains for both opposing and following movements on the same track. 

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A Traffic control system (TCS) is a form of railroad signaling that allows trains to operate on signal indication as their only authority.  TCS consolidates train routing decisions that were previously carried out by local signal operators or the train crews themselves to a single dispatcher in a central office.  One characteristic TCS is a control display graphical depiction of the railroad. On this display the dispatcher can keep track of trains' locations across the territory that the dispatcher controls.  Larger railroads may have multiple dispatcher's offices and even multiple dispatchers for each operating division.   The BNSF, CSX, and Union Pacific all have large centralized dispatching offices.

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TCS combines Two Proven Technologies

Interlocking

Automatic Block

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And adds in a communications system.

Traffic Control Systems

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Traffic Control Systems

This is a typical TCS control point.  It consists of a track turn-out, a power operated switch, and the four signals (one for each route) that govern movement over the switch.  This diagram also shows the three approach signals to the control point.

Before a proceed signal can be displayed by any of the absolute signal (Sig. 1.1, 2.1, 3.1a, and 3.1b) certain conditions must be met.  Those conditions are:
          - The switch point must be within 1⁄4 inch of full normal or reverse. (236.303)
          - The switch must be locked. (236.307)
          - The “OS” trach circuit (including the fouling section) must be unoccupied. (236.201)
          - The next track circuit in advance of the “OS” track must be unoccupied. (236.201)(236.311)
          - No opposing traffic is allowed in the block ahead. (236.405)
          - The plant cannot be “in time”. (236.407)

Also, applicable to a TCS system are the following:
          - 236.309	Loss of shunt protection; where required.
          - 236.310	Signal governing approach to home signal.
          - 236.202	Signal governing movements over hand-operated switch.
          - 236.203	Hand-operated crossover between main tracks; protection.
          - 236.205	Signal control circuits; requirements.
          - 236.206	Battery or power supply with respect to relay; location.

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Standards

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Following are the standards to which all traffic control systems must be designed, installed, tested, and maintained.

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236.401   Automatic block signal system and interlocking standards applicable to traffic control systems.
        - 236.201 Track-circuit control of signals.
        - 236.202 Signal governing movements over hand-operated switch.
        - 236.203 Hand-operated crossover between main tracks; protection.
        - 236.205 Signal control circuits; requirements.
        - 236.206 Battery or power supply with respect to relay; location.
        - 236.303 Control circuits for signals, selection through circuit controller operated by switch points or by switch locking mechanism. 
        - 236.307 Indication locking.
        - 236.309 Loss of shunt protection; where required.
        - 236.310 Signal governing approach to home signal.
        - 236.311 Signal control circuits, selection through track relays, or devices functioning as track relays, and through signal mechanism contacts...

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This rule prescribes the following automatic block signal system and interlocking standards be applied to traffic control systems:

236.201	Track-circuit control of signals.

236.202	Signal governing movements over hand-operated switch.

236.203	Hand-operated crossover between main tracks; protection.

236.205	Signal control circuits; requirements.

236.206	Battery or power supply with respect to relay; location.

236.303	Control circuits for signals, selection through circuit controller operated by switch points or by switch locking mechanism.

236.307	Indication locking.

236.309	Loss of shunt protection; where required.

236.310	Signal governing approach to home signal.

236.311	Signal control circuits, selection through track relays, or devices functioning as track relays, and through signal mechanism contacts and time releases at automatic interlocking.

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236.402   Signals controlled by track circuits and control operator.

The control circuits for home signal aspects with indications more favorable than "proceed at restricted speed'' shall be controlled by track circuits extending 

through entire block.

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This standard requires that all home signal aspects more favorable than "proceed at restricted speed" be controlled by track circuit extending through the entire block.  At a controlled point the control circuits may be controlled by a control operator and at manually operated interlockings the home signals shall be controlled manually in cooperation with control operator.

Any aspect more favorable than "proceed at restricted speed" must be selected through track relays regardless of any speed limit or restriction.  The aspects and indications of the governing signals determine compliance with this standard, not the authorized train speed.

A block extends from a signal to the next governing signal or from a signal to the limits or end of the system.  The end of the system, absent a signal, may be identified by the use of wayside signage, or by specific designation in the carrier’s timetable or special instructions.

Control circuits do not have to be manually controlled by the operator and may be automatic. However, it is not the intention of this rule to give control to any other individual operation in opposition to or in conflict with the control operator.

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Signals controlled by track circuits

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Track Circuits

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Interlocked Signal Definition

§ 236.807 Interlocked Signal

A roadway signal which governs movements into or within interlocking limits. 

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Signals at TCS control points are interlocked signals and must be controlled by track circuits through the entire block governed by the signal.

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236.403   Signals at controlled point.

Signals at controlled point shall be so interconnected that aspects to proceed cannot be displayed simultaneously for conflicting movements...

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except that opposing signals may display an aspect indicating "proceed at restricted speed at the same time on a track used for switching movements only, by one train at a time.

This rule requires signals at a controlled point to be so interconnected that aspects to proceed cannot be displayed simultaneously for conflicting movements, except they may display an aspect indicating "proceed at restricted speed" at the same time on track used for switching movements only.

Signals at every controlled point must be so interconnected that aspects to proceed cannot be displayed simultaneously for conflicting train movements.

This is a companion rule to Section 236.308 in that it permits display of aspect indicating "proceed at restricted speed" at the same time on track used for switching movements only by one train at a time.

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Signals for Conflicting Routes

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Conflicting Routes Definition

§ 236.796 Conflicting Route

Two or more routes, opposing, converging or intersecting, over which movements cannot be made simultaneously without possibility of collision. 

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Signals at TCS control points are interlocked signals and must be controlled by track circuits through the entire block governed by the signal.

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Opposing Signal Definition

§ 236.808 Opposing Signals.

Roadway signals which govern movements in opposite directions on the same track. 

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236.404   Signals at adjacent control points.

Signals at adjacent controlled points shall be so interconnected that aspects to proceed on tracks signaled for movements at greater than restricted speed cannot be displayed simultaneously for conflicting movements.

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This rule requires that signals at adjacent controlled points to be interconnected so that aspects to proceed on tracks signaled for movements at greater than restricted speed cannot be displayed simultaneously for conflicting movements.

This rule permits restricted speed aspects to be displayed simultaneously for opposing or converging routes at adjacent control points provided the speed restrictions between the control points do not exceed 20 mph.  The rule was revised in 1964 primarily to permit restricted speed conflicting movements into a siding from each end.  The maximum authorized speed between adjacent controlled points where signals can simultaneously display aspects indicating proceed at restricted speed shall not exceed 20 mph regardless of more favorable aspects displayed and regardless whether or not track is signaled.

Signals at adjacent control points.

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Block Signal Definition

§ 236.804 Block Signal

A roadway signal operated either automatically or manually at the entrance to a block. 

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The signals governing movement into the block from an adjacent control point are block signals and cannot simultaneously display aspects greater than proceed at restricted speed.

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236.405   Track signaled for movements in both directions, change of direction of traffic.

On track signaled for movements in both directions, occupancy of the track between opposing signals at adjacent controlled points shall prevent changing the direction of traffic from that which obtained at the time the track became occupied...

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except that when a train having left one controlled point reaches a section of track immediately adjacent to the next controlled point at which switching is to be performed, an aspect permitting movement at not exceeding restricted speed may be displayed into the occupied block.

This rule prevents the changing of the direction of traffic from that which was obtained at the time the track was occupied between opposing signals at adjacent controlled points on track signaled for movement in both directions except that when a train having left one controlled point reaches a section of track immediately adjacent to the next controlled point at which switching is to be performed, an aspect permitting movement at not exceeding restricted speed may be displayed into the occupied block.

This rule requires that traffic control systems have nearly the functional equivalent as that of “traffic locking” installed and operating properly and as intended however, there is no requirement for testing it as prescribed by Section 236.381.

After a train or engine has passed a signal displaying an aspect permitting it to proceed into and through a controlled point, the opposing signals at the adjacent controlled point shall not display any aspect with an indication other than "stop", as long as the section of track between controlled points is occupied.

Rule 236.405's exception to the traffic locking requirements applies only in instances when a train is left on the main track while its engine and/or cars move into an adjacent siding or yard for switching purposes and must, in returning to its train, reverse its direction for a short distance.  It is permissible in such instances to permit such movements to be made with a signal aspect indicating "proceed not to exceed restricted speed" into the occupied block.

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Signals at adjacent control points.

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Direction of Traffic

Change Direction of Traffic

Control Point Definition

§ 236.782 Control Point

A location where signals and/or other functions of a traffic control system are controlled from the control machine. 

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236.407   Approach or time locking; where required.

Approach or time locking shall be provided for all controlled signals where route or direction of traffic can be changed.

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This rule requires that approach or time locking be provided for each controlled signal where route or direction of traffic can be changed.

This rule applies to all controlled signals at controlled points where route can be changed or where direction of traffic can be changed.  Does not apply to so called "holding signals" between controlled points where the direction of traffic cannot be changed. 

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Approach or time locking; where required.

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This rule applies to all signal governing movement into and through control points.

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Time Locking Definition

§ 236.768 Time Locking 

A method of locking, either mechanical or electrical, which, after a signal has been caused to display an aspect to proceed, prevents, until after the expiration of a predetermined time interval after such signal has been caused to display its most restrictive aspect, the operation of any interlocked or electrically locked switch, movable-point frog, or derail in the route governed by that signal, and which prevents an aspect to proceed from being displayed for any conflicting route. 

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Time locking

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Time Locking

Once a train route has been cleared with a proceed signal, if the signal is subsequently set to “Stop” the route must remained locked until a predetermined time has expired.

For example, The following event have occurred:

The switch has been reversed and locked.

The “OS” track is unoccupied.

Block 1 is unoccupied.

Signals 1.1, 3.1a, and 3.1b are at “Stop” and not in time.

This has allowed Signal 2.1 to be cleared for a diverging route into the siding.  

If the dispatcher changes his mind and sets Signal 2.1 to “Stop” a predetermined time must expire before the dispatcher can change the route (move the switch or clear another signal).

The predetermined time is calculated by how long it would take a train to travel from a point 1500 feet in approach to the approach signal to the home signal at a speed of 221⁄2 mph.

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Approach Locking Definition

§ 236.760 Approach Locking

Electric locking effective while a train is approaching, within a specified distance, a signal displaying an aspect to proceed, and which prevents, until after the expiration of a predetermined time interval after such signal has been caused to display its most restrictive aspect, the movement of any interlocked or electrically locked switch, movable-point frog, or derail in the route governed by the signal, and which prevents an aspect to proceed from being displayed for any conflicting route. 

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Approach locking

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Predetermined

Time must expire.

5 sec. Loss of shunt time only

on “OS” track circuit.

Once a train route has been cleared with a proceed signal, if the signal is subsequently set to “Stop” the route must remained locked until a predetermined time has expired, unless there is no train on the approach to the signal.  If no train is on the approach only a 5 second loss of shunt protection time must expire before the route can be changed.

For example, The following event have occurred:

The switch has been reversed and locked.

The “OS” track is unoccupied.

Block 1 is unoccupied.

Signals 1.1, 3.1a, and 3.1b are at “Stop” and not in time.

This has allowed Signal 2.1 to be cleared for a diverging route into the siding.  

If the dispatcher changes his mind and sets Signal 2.1 to “Stop” nd a train is on the approach to Signal 2.1, a predetermined time must expire before the dispatcher can change the route (move the switch or clear another signal).  

However, if there is no train on the approach to Signal 2.1 only a 5 second loss of shunt time must expire before the route can be changed.

The predetermined time is calculated by how long it would take a train to travel from a point 1500 feet in approach to the approach signal to the home signal at a speed of 221⁄2 mph.

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236.408   Route locking.

Route locking shall be provided where switches are power‐operated.  Route locking shall be effective when the first pair of wheels of a locomotive or car passes a point not more than 13 feet in advance of the signal governing its movement, measured from the center of the signal mast or, if there is no mast, from the center of the signal.

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This rule specifies where route locking shall be provided and where it shall become effective in the route entered.

At any location in traffic control territory where switches are power-operated, route locking must be provided and it must be effective when the first pair of wheels of a locomotive or car passes a point 13 feet in advance of the signal governing its movement.  

The 13 feet shall be measured from the center of the signal mast portion on which it is mounted (e.g. from center of tall mast, or of off-set or dummy mast), to the effective insulated joint.  Where the signal is not mounted on a vertical ground mast, the 13 feet shall be measured from the center of the signal.  This rule does not apply to automatic signals or controlled signals that do not have power-operated switches in the route governed.

Route locking is not required nor provided where there is an absence of a power-operated switch, movable-point frog, or derail in the route.  Route locking is also not required by this rule in an instance of a train crew receiving permission to pass a stop signal indication (i.e., occupancy of the track circuit(s) alone lock the switch).  Where any location is found not having the equivalent of route locking in that instance, and it is equipped with one or more dual-controlled power-operated switches, assurance should be gained that the carrier’s special instructions for hand-operation of such a switch provide for the safe movement of trains (e.g., the switch may not be restored to power operation until the rear of the train has passed over and beyond it.)

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Route locking

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Once a train has entered to route on a proceed signal that route must remained locked until the complete movement has been accomplished.

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Route Locking Definition

§ 236.767 Route Locking.

Electric locking, effective when a train passes a signal displaying an aspect for it to proceed, which prevents the movement of any switch, movable-point frog, or derail in advance of the train within the route entered. It may be so arranged that as a train clears a track section of the route, the locking affecting that section is released. 

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Within interlocking limits route locking shall be effective at a point not more than 13 feet in advance of the signal measured from the center of the signal mast portion on which it is mounted, or if there is no mast, from the center of the signal.

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236.410   Locking, hand-operated switch.
        - Each hand‐operated switch in main track shall be locked either electrically or mechanically in normal position, except:...
        - Approach or time locking shall be provided and locking may be released either automatically, or by the control operator...

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This rule requires that hand-operated switch in main track be locked either electrically or mechanically in normal position, or a signal be provided to govern train movements to the signaled track.  It exempts those hand-operated switches on main track where train speeds do not exceed 20 mph, on signaled sidings without intermediate signals where train speeds do not exceed 30 mph, or where trains are not permitted to clear the signaled track.  It requires approach or time locking and provides that locking may be released either automatically or by the control operator after the control circuits of signals governing movements over the switch have been opened directly or by shunting of track circuit.

Any signaled track in traffic control territory is considered as main track.  If speed on main track, except signaled sidings, exceeds 20 miles per hour, each hand-operated switch must comply with this section.  Speed may be controlled by permanent speed zone or by signal indication.

Sidings provided with signal protection and without intermediate signals are signaled sidings. If train speed exceeds 30 mph on a signaled siding, each hand-operated switch on such siding must comply with this section.

Hand-operated switches are not required to be locked where trains are not permitted to clear the main track.  Trains may enter such switches provided a car is left on main track, the switch is left open, or derail equipped with switch circuit controller is left in non-derailing position.  Note that this option may not be available to the railroad where a siding track, equipped with a hand-operated switch on either end, spans an intermediate or control point signal location.  The reason it is not available is that even though a train may not clear one end (leaving a portion of the train on the main track or leaving the switch thrown reverse), and the signal governing movement over the switch at that end will therefore be displaying its most restrictive indication, the signal governing movement over the switch at the other end of the siding track in which the train is located may not be displaying its most restrictive indication (equivalent to the train being “cleared” in that track). 

Approach or time locking must be provided for each lock, must be effective, and must be installed in such a manner that it cannot be defeated by any action of train crew members (except via operation of an emergency release device, if so equipped, and as addressed below.)

Locks may be provided with emergency release device which must be kept sealed.  Emergency release device with broken or missing seals, except such release device with latch out feature that opens signal control circuits until reset by signal maintainer, is prohibited.

Lock may be released either automatically or by control operator.  Control circuits of signals governing movements over the switch which display aspects more favorable than "Proceed at Restricted Speed" must be opened, or track circuit must be shunted before locking is released.

Electric or mechanical lock provided with time locking must not release until after expiration of a predetermined time interval sufficient to permit a train, having passed the signal governing movement over the switch displaying an aspect with an indication more favorable than proceed at restricted speed, to pass the switch; or, to permit a train approaching the signal governing movement over the switch displaying an aspect of "stop" or "stop and proceed", to stop, or where the signal governing movement over the switch displays a "restricting" aspect, to permit the train to reduce to restricted speed.

Electric or mechanical lock provided with approach locking must not release when approach section is occupied until after expiration of a predetermined time interval sufficient to permit a train to stop or to pass the switch, or where signal governing movement over the switch displays "restricting" as its most restrictive aspect, the train can reduce its speed to restricted speed.  If approach section is unoccupied, lock may release immediately after signal control circuits are opened.

Control circuit for electric lock must be so arranged and installed that shunting of turnout will not release lock for movement to main track.

Locking member of electric or mechanical lock must be so maintained that it cannot be displaced from its locked position by quickly operating the lock lever or pedestal.

Where signal is provided in lieu of a lock to govern train movements to signaled track, an aspect permitting a train to proceed shall not be displayed until the control circuits for all signals governing movement over the switch on the signaled track are opened, and approach circuits in both directions are unoccupied, or a predetermined time interval has expired.

Where exception (1) is relied upon, it is permissible for trains, after approaching the switch at speeds not exceeding 20 miles per hour, to accelerate after the locomotive occupies the switch points.

The provision of exception (2) does not apply to maintenance-of-way work equipment.  Such maintenance-of-way equipment as motor cars and track machinery such as tampers, liners, burro cranes with or without cars, Sperry test car, and Speno Rail Grinder equipment is not considered to be a train, and may clear the main track in TCS territory without regard to requirements of this rule.

A footnote to this rule requires that all hand-operated switches in traffic control territory be brought into compliance with these provisions on or before December 31, 1986.

Rules and Instructions

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236.426   Interlocking rules and instructions applicable to traffic control systems.
        - 236.327	Switch, movable-point frog split-point derail.
        - 236.328	Plunger of facing-point lock.
        - 236.330	Locking dog of switch-and-lock movement.
        - 236.334	Point detector.
        - 236.342	Switch circuit controller.

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The rules and instructions prescribed in  236.327 and 236.328,  236.330 to  236.334, inclusive, and  236.342 shall apply to traffic control systems.

This rule prescribes the following interlocking inspections and tests be made of traffic control systems.  (See Technical Bulletin S-04-01)

 236.377	Approach locking.

 236.378	Time locking.

 236.379	Route locking.

 236.380	Indication locking.

 236.382	Switch obstruction test.

 236.383	Valve locks, vales and valve magnets.

 236.386	Restoring feature on power switches.

Results of tests shall be recorded in compliance with Rule 236.110.

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Review

These are the Subpart B standards that apply to TCS:
        - 236.201 Track-circuit control of signals.
        - 236.202 Signal governing movements over hand-operated switch.
        - 236.203 Hand-operated crossover between main tracks; protection.
        - 236.205 Signal control circuits; requirements.
        - 236.206 Battery or power supply with respect to relay; location.

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Review

These are the Subpart C standards that apply to TCS:
        - 236.303 Control circuits for signals, selection through circuit controller operated by switch points or by switch locking mechanism. 
        - 236.307 Indication locking.
        - 236.309 Loss of shunt protection; where required.
        - 236.310 Signal governing approach to home signal.
        - 236.311 Signal control circuits, selection through track relays, or devices functioning as track relays, and through signal mechanism contacts...

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Review

These are the Subpart D standards that apply to TCS:
        - 236.402 Signals controlled by track circuits and control operator.
        - 236.403 Signals at controlled point.
        - 235.404 Signals at adjacent control points.
        - 236.405 Track signaled for movements in both directions, change of direction of traffic.
        - 236.407 Approach or time locking; where required.
        - 236.408 Route locking.
        - 236.410 Locking, hand-operated switch.

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S&TC  FUNDAMENTALS

49 CFR 236

Subpart D

Traffic Control Systems 

The End

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